Give me a call at 804-833-6418 John.
100-120 miles. I'm sure it has to do with the caulks used on the ridge. I've seen plenty of evidence, but don't know which brands cause the most damage.
Others and myself have used and seen bibs used 30+ years under slate. .019 and thinner. I was going to use 20oz. copper until I opened this one up. All the 20 oz. is burned out. I may switch to black aluminum, or a small hemmed piece of black 'trim' covering the steps. I did that some years ago on a severe one and it worked fine. Once, I saw a new valley burning real bad after a year. I painted the darn thing black. At least it then matched the original black painted galv. Fighting nature here, not a normal 'leak/no leak' situation.
Acid rain has gotten worst over the years. I may put a hemmed apron over the steps out of aluminum and shoo for 40+ years.
This is news to me, we just finished a 1910's house that had copper step,counter and valleys. It was in great shape. Just replaced the step because of the number of nail holes. :cheer: